AI War:Wormhole Guard Post

These massively-armored guard posts have practically no guns, but stand sentinel over wormholes that the AI controls. They are destroyed when the command station is destroyed -- attacking them head-on is usually a waste of time.

This special guard post is only allowed to appear beside wormholes. The number of wormhole guard post on each wormhole depends on AI difficulty and type. The Bouncer AI Type replaces all wormhole guard posts with regular guard posts.

How to counter when in the AI fleet

As the description mentions, these guard posts are generally ignored.
Indeed, your ships will not auto-attack them and require manual targeting via right-click to be attacked.
If you really need the warp point they are guarding to receive no further reinforcements you can destroy these, just expect even a large fleet to take several minutes to do so.